The invention relates to a circuit arrangement for effecting quick-charging of a battery.
More particularly, the invention relates to circuit arrangements of this type in which a voltage source is connected to the battery by a first controllable electronic switch, and in which a second controllable electronic switch renders the first switch conductive or non-conductive in dependence upon the charging voltage or the charging current of the battery.
Quick-charge circuits of this type operate with a high charging current, which normally leads relatively soon to reaching of the gassing voltage of the battery. If the gassing voltage is reached, further charging of the battery can result in its destruction. Accordingly, in order to achieve a quick but nevertheless safe charging of the battery, it is necessary to switch over from the high-amperage quick-charge charging current to a low-amperage trickle-charge charging current shortly before the gassing voltage is reached. The voltage at which this switchover should occur is referred to herein as the switchover voltage.
The value of the gassing voltage is not a constant, but depends upon the type of battery involved, the ambient temperature, and the charging current or the voltage producing the charging current.
It is already known to provide a quick-charge charging circuit so designed that a switchover to the trickle-charging occurs shortly before the gassing voltage of the battery is reached. This known arrangement adequately takes into account the effect of temperature upon the value of the gassing voltage, upon the electronic switchover component, and upon the charging voltage applied directly across the battery. However, it does not take into account the effect upon the switchover of fluctuations in the voltage applied across the input terminals of the charging circuit and accordingly of the charging current. If the voltage applied to the input terminals of the charging circuit briefly increases or decreases, then with the known charging circuit, an elevated or reduced charging voltage is simulated, and the circuit improperly switches over from quick-charge to trickle-charge, or vice versa. The possibility of such improper switchover is to be avoided, because supply voltage fluctuations of the type in question are frequently encountered when utilizing utility-company mains voltages. Improper switchover can result also from supply voltages which do not fluctuate but protractedly have a magnitude or amplitude higher or lower than anticipated by the designer of the charging circuit.